The present invention relates to polycrystalline abrasive grit, to a method for making the abrasive grit and to tools having a cutting or abrading surface wherein the abrasive grit is held in a binder. A tool of the present invention may be a drill bit or dressing tool or an impregnated tool such as a grinding wheel, saw, honing stone or the like.
Methods and apparatus for making polycrystalline diamond or cubic boron nitride (CBN) compacts are well known. For example, methods for making diamond compacts are taught in U.S. Pat. No. 3,141,746, July 21, 1964 to DeLai, and in later U.S. Pat. Nos. 3,609,818, Oct. 5, 1971, and 3,745,623, July 17, 1973, both to Wentorf, Jr., et al, and 4,224,380, Sept. 23, 1980 to Bovenkerk, et al. A method for making a CBN compact is taught in U.S. Pat. No. 3,767,371, Oct. 23, 1973 to Wentorf, Jr., et al.
Generally speaking, polycrystalline diamond or CBN compacts are made by high-pressure, high-temperature processing wherein diamond or CBN particles are compressed and heated in the presence of a metallic catalyst or sintering aid material. Under the proper pressure and temperature conditions, diamond to diamond or CBN to CBN bonds are catalyzed to bond the diamond or CBN particles together in a polycrystalline compact. The resulting polycrystalline compact can then be used as an abrasive tool or can be subjected to still further process steps.
One further process step involves leaching non-diamond or CBN material from the compact. For example, U.S. Pat. Nos. 4,224,380, Sept. 23, 1980 to Bovenkerk, et al, and 4,104,344 to Pope, et al, teach chemically leaching non-diamond material such as sintering aid or catalytic material to provide a polycrystalline compact consisting essentially of self-bonded, abrasive particles with a network of inter-connected, empty pores dispersed throughout.
In accordance with the present invention, a polycrystalline diamond or CBN compact is subjected to leaching and size reduction steps to provide polycrystalline abrasive grit having substantially uniform physical properties; for example, abrasion resistance and fracture toughness properties. Thus, the present invention facilitates production of tools with abrasive grit of substantially uniform, consistent physical properties. The present invention also facilitates the selection of abrasive grit having the specific physical properties desired for a specific use. Weak polycrystalline grit particles are separated from stronger polycrystalline grit during the process of this invention. Furthermore, each polycrystalline grit comprises a plurality of self-bonded randomly oriented crystals. Hence, the polycrystalline grit can be employed in a tool having consistent strength and hardness characteristics. A tool of the present invention is an improved tool enjoying advantages of improved mechanical bond strength between the grit particles and the binder which can be a resin, metal, plated or vitreous binder. Further understanding of the present invention will be obtained from the following disclosure.